convertibility vs inconvertible

convertibility is a noun but inconvertible is not a noun.

Word	Noun	Adjective	Verb	Adverb
convertibility	Yes	No	No	No
inconvertible	No	Yes	No	No

convertibility (noun)	inconvertible (noun)
the quality of being exchangeable (especially the ability to convert a currency into gold or other currencies without restriction)

convertibility (adjective)	inconvertible (adjective)
	used especially of currencies; incapable of being exchanged for or replaced by another currency of equal value
	not capable of being changed into something else